Small-number duplication of trial manufacture model and small-amount production of duplicate model have heretofore been conducted by producing a mold from a silicone rubber with a master model, casting a thermosetting resin into the mold in vacuum, and thermosetting the cast resin. This thermosetting resin is ordinarily a two-pack type and the time from mixing of the two packs to the start of setting (curing) is short; therefore, there have been problems that the casting of the thermosetting resin into the silicone rubber-made mold must be conducted in a short time and moreover, even if the casting is conducted with care, curing starts during the casting operation to generate defective in some cases. There have also been problems that the container used for mixing or casting of the thermosetting resin must be washed each time after the use before the resin is cured (this requires a complicated operation) and, moreover, a long time of about 2 hours is required for the heat-curing of the thermosetting resin (this restricts the times of duplication per day).
Meanwhile, JP-A-58-80587 discloses a method for duplication of plastic case for watch by casting an ultraviolet-curing one-pack type synthetic resin for cast molding into a transparent mold made of a silicone rubber or the like and applying an ultraviolet light under vacuum. In this method, as the ultraviolet-curing resin, there are used a synthetic resin (e.g. spiran resin) for cast molding containing benzophenone as sensitizer, a reaction accelerator-containing unsaturated polyester resin, etc.
Further, JP-A-3-114711 proposes a method for casting a photosensitive resin into a transparent silicone rubber mold and applying an ultraviolet light to cure the resin, wherein the photosensitive resin is a mixture of diacrylate of bisphenol A-ethylene oxide adduct, acrylate of phenyl glycidyl ether and a photopolymerization initiator.
Further, JP-A-7-124962 proposes a method for producing a plastic molded article, which method comprises the steps of casting, into a transparent silicone rubber made mold, an active energy ray-curing liquid resin composition comprising a urethanepoly(meth)acrylate having at least two (meth)acryloyloxy groups, a particular diallyl compound, an aliphatic polythiol compound having at least two thiol groups, and an active energy ray polymerization initiator, and irradiating the above liquid resin composition with an active energy ray to cure the resin composition.
Furthermore, the present applicant proposed a photosensitive resin composition wherein the cracking tendency of the above photosensitive resins is alleviated (JP-A-8-244044 and JP-A-8-323778).
While duplicate models produced by cast molding are required to have a high dimensional accuracy, there have remained a problem that the dimension of duplicate model produced with a photosensitive resin is smaller than the dimension of master model because the photosensitive resin gives rise to shrinkage during ultraviolet curing. The shrinkage can be made up for by making a master model of larger size, but production of a trial manufacture model for initial shape evaluation and a master model used for duplication, in different dimensions results in low efficiency, which has restricted the applications of such an approach.
Duplicate models of trial manufacture model are desired, in some cases, to have, for example, an opaque white color such as possessed by ABS, depending upon the application. However, addition of, for example, titanium oxide, carbon black or the like to a photosensitive resin in order to allow the resin to have an opaque color results in reduced photosensitivity, which restricts the maximum possible thickness of duplicate model; thus, allowing a photosensitive resin to have opaqueness with no problems has been difficult. Coloring of duplicate model by coating has also been conducted. This, however, has had problems in that the coating step increases the number of total operational steps and the chipping, flaking, or peeling of coating applied, when occurring, makes the duplicate model look bad.
When the photosensitive resin composition casted into a silicone rubber mold is irradiated, for curing of the resin composition, with an ultraviolet light emitted from an exposure apparatus whose light sources are provided above and below the mold, such as used in production of printing plate, there has been a problem in that the portions of the resin composition corresponding to the sides of model produced are not sufficiently cured, generating defectives.
In producing a mold with a silicone rubber, a long time of 10 hours or more is required to cure the mold. Therefore, a silicone rubber curable in a shorter time has been desired by model producers who wish to produce and evaluate duplicate models in a period as short as possible after the designing of trial manufacture model.
Objects of the present invention are to provide, in a method for production of duplicate model by producing an ultraviolet-transmittable silicone rubber-made mold using a master model, casting a photosensitive resin composition into the mold, and applying an ultraviolet light to cure the resin composition, a photosensitive resin composition for cast molding which enables production of a duplicate model having high dimensional accuracy, high hardness and cracking resistance, and also a photosensitive resin composition for cast molding which enables production, by ultraviolet curing, of even a duplicate model having an opaque color and yet a large thickness. Other object of the present invention is to provide a photosensitive resin composition for cast molding which is suitable for production of a duplicate model in a simple operation in a short period. Still other object of the present invention is to provide a method for production of a duplicate model, which uses an exposure apparatus capable of producing a completely cured three-dimensional model.